gibson



Y 1931. G. H. GIBSON 1,806,970

COMBUSTION REGULATION 'Filed Jfily 22.1929

IN VEN-TOR. GEORGE h. 6/550 ATTORNEY Patented May 26, 193i AENT OFFICE GEORGE E. GIBSOIlhOF UPPER MQNTCLAIR, NEW JERSEY COMBUSTION REGULATION Application filed July 22,

The present invention relates to combustion control systems for furnaces and particularly for steam generator furnaces, and the general objectof my invention is to provide an improved combustion control system for a furnace characterized by its effectiveness, operative simplicity, and capacity for the attainment of the objects hereinafter set forth.

A primary object of the invention is to provide an improved method of and apparatus for regulating the supply of air to a furnace in automatic-response to some furnace condition, such as the furnace temperature, which is a measure or indication of the eficiency of combustion in the furnace, to thereby obtain and maintain a desirably high furnace combustion efficiency.

A further object of my invention is the provision of simple and efiective control apparatus for automatically controlling the draft regulating mechanism of the furnace, the effective control action of the apparatus being determined by the result of previous control actions.

ln furnaces in which solid fuel is burned on a stationary or movable grate, regardless of whether all of the air for combustion is supplied at one side of the fuel bed or partly at one side and partly at the other, the eficiency of combustion is affected by the varying resistance of the fuel bed to gas flow therethrough. In normal operation the fuel bed resistance is continually changing in a mannor which cannot be foretold or determined with precision. When the fuel bed is thick ened, as by increasing the rate at which fuel is supplied, an increase in furnace draft is ordinarily required to avoid a decrease in 40 combustion efiiciency, but a regulation of the furnace draft in proportion to the rate of fuel supply does not always or necessarily maintain a desirably high furnace efliciency. The maintenance of a high furnace efiiciency requires a draft which will supply sufficient air to affect combustion of practically all p the combustible gases rising from the fuel bed and yet which will not supply excess air in amount suflicient to objectionably lower the temperature and increase the weight of the lil 1929. Serial No. 880,121.

heating gases. As already explained, the desirable draft which actually supplies the exact amount of air giving the highest furnace eficiency at any instant, depends on the fuel bed resistance at that instant. In general, a high furnace temperature, indicates efficient combustion, and also that a large amount of heatgenerated is available for absorption in the urnace. While a. high CO content in the flue gases normally indicates eficient com.- til) bustion, it is possible to have a high CO content when an appreciable portion of the fuel is being burned to CO with resultant heat generation of approximately only one third that which would be obtained if the fuel was 5 being burned to (30 It is therefore sometimes desirable to increase and at other times desirable to decrease the rate of air supply when the CO content in theflue gases is high and also when that content is low to obtain a 79 desirably high furnace efioiency.

In accordance with the present invention I provide apparatus whereby, regardless of the general rate of combustion desired, a regulating effectis exerted normally tending to regularly and continuously vary the rate at which air is supplied. When the furnace temperature, or other furnace condition utilized in obtaining the regulating efiect, indicates a decrease in furnace efliciency, I alternately 3 increase and decrease the rate of air supply until the condition is attained in which the furnace efiiciency begins to increase, after which the rate of air supply is changed in the same direction as itwas changingwhen the furnace efficiency began to increase. This change in the rate of air supply may be continued in the same direction until the furnace efliciency again begins to fall, but preferably the rate changing effect is arrested, if and when the furnace efficiency reaches a predetermined value which is, or is assumed to be, a practical maximum.

The furnace condition which I regard as best adapted for utilization in regulating combustion in accordance with the present invention, is the furnace chamber temperature,

as it ordinarily approximates a maximum vwhen the maximum practical furnace efliciency is obtained. The draft changing effect is preferably utilized in a combustion regulating system having provisions for making the general rate of combustion dependent on the furnace load and the present invention also comprises novel provisions for this purpose. Such provisions tend to maintain a rate of air supply, which may be called the base rate, proportional to the furnace load.

In operating such a furnace system, the base rate of air supply is varied in accordance with the present. invention to obtain and maintain the desired high furnace efliciency.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, and the advantages possessed by it reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

Of the drawing:

Fig. 1 is a diagrammatic representation of a steam generator furnace combustion control system.

In Fig. 1 I have illustrated one embodiment of my invention in which fuel is supplied to a furnace A of a steam generator by a stoker mechanism B including an electric driving motor B, and in which air for combustion of the fuel is supplied to the furnace by a forced draft fan C driven by an electric motor C, and in which a throttle damper C in the conduit O through which the air passes from the fan to the furnace, is adjusted in accordance with the present invention to vary the effective furnace draft in automatic response to the furnace chamber temperature. The temperature of the furnace chamber is measured by a thermocouple D connected to the control apparatus as hereinafter described. In the apparatus shown in Fig. 1 the general rate of furnace combustion is made automatically proportional to the furnace load by suitable provisions for regulating the speeds of the motors B and G.

The provision shown for thus operating the motors B and C of each steam generator at speeds proportional to the load comprise a device E for simultaneously adjusting resistances in the energizing circuits of the stoker and fan motors B and C respectively, in response to variations in the steam pressure in a steam main or header A. As shown the device E comprises a pressure chamber E one wall of which is formed by a flexible diaphragm E and to which a pipe E transmits the pressure of the steam in the main A which receives the steam generated from all or a portion of the steam generator units in theplant. The outward movement of the diaphragm E is opposed by a lever E fulcrumed at E and carrying a suitable adjustable counterweight E the position and weight of which fixes the steam pressure which the controller E tends to maintain and at which a contact E on the lever occupies its normal position between a pair of stationary switch contacts and F. On arisein steam pressure above the normal, the contact E engages the contact F. This closes one of the two circuits for energizing a reversible relay motor F from suitable electric supply mains 1 and 2. The circuit thus closed includes a conduit 3 running to the contact E from the supply conduit 1, a conductor 4 running to one terminal of the motor F from the supply conductor 2, and a conductor 5 running from the switch contact F to a second terminal of the motor F The motor F forms the actuator of a contact bar G mounted on a threaded extension F of the motor shaft. The contact bar is connected by a conductor 7 to the supply conductor 2. The movements of the contact arm are guided by stationary guide bars G, on which the ends of the contact are slidably mounted. The contact arm is adapted to move over the surface of a rheostat body H on which re- .1'

sistances R, R R and R are supported, the resistances R and R being in the energizing or control circuits of the stoker and fan motors, respectively.

The energizing or control circuit for the stoker motor comprises the conductor 7 connected to the supply conductor 2, the contact bar G, resistance R, and a conductor 8 to one terminal of the motor and a conductor 9 to the supply conductor 1 from the other terminal of the motor. The energizing or control circuit of the fan motor C comprises the conductor 7 from the supply conductor 2, contact bar G, resistance R and a conductor 10 to one terminal of the motor and a conductor -11 from the other terminal of the motor to the supply conductor 1.

On a rise in the steam pressure which brings the contact E into contact with the contact F, the motor F 2 rotates in the direction required to raise the contact bar G, thus increasing the amount of the resistance R in the energizing circuit of the motor B and increasing the amount of the resistance R in the energizing circuit of the motor C. This decreases the speeds of the motors B and C with a consequent reduction in the rate of air and fuel supply and the rate of combustion, so that the steam pressure will be brought down to normal. On a fall in steam pressure below normal, the contact E engages the contact F and energizes the second winding of the reversible motor F through a conductor 6. The motor is then rotated in the direction required to lower the contact bar Grand thereby decrease the amounts of the resistances R and R in the energizing circuits of the motors B and O. The speed of the motors is thereby increased with a corresponding increase in the rate of combustion as required to restorethe steam pressure to its desired value. A rheostat R in the energizing circuit for the motor B and a rheostat R in the energizing circuit for the motor C permit of an independent adjustment of the speed of each motor and make it readily possible to vary the ratio of the speeds dll of these motors normally maintained by the operation of the pressure responsive device E.

When arranged as described, the controller E will tend to hold a constant pressure in the steam main A by a direct quick acting regulation and would therefore be unstable. To overcome this unstability the controller E is temporarily acted upon by a compensating means or loading force which tends to render the controller more stable without atfecting the sensitivity thereof. Compensating means for this purpose may comprise an electric dynamometer J of the Kelvin balance type having spaced stationary coils J located at opposite sides of a floating coil 3. The coils J and J are connected in series in the conductor 8 between the resistance R and one terminal of the stoker motor B. A member J is rigidly connected to the floating coil J 2 and transmits the movement of the latter to acontainer or bucket J suspended by a coiled spring J 5 from a suitable support. A similarly shaped container J of smaller size is suspended within the container J by alink J connected to the lever E atone end thereof. The containers J andJ are partially filled with a suitable liquid such as water or a light oil. The bucket J 6 is provided with an adjustable orifice J adjacent the bottom thereof and through which the liquid'levels in the containers are equalized. The various portions of the compensating apparatus are so proportioned that when the lever contact E is in its intermediate position and the steam pressure in the main A is at the desired value, the liquid levels in the containers will be the same and the container J partly immersed in the container J as shown in the drawing.

With the control apparatus and compensating means arranged as described, the liqaid in the containers J and J is at the same level, if the pressure in the steam main has been at the desired value for a sufiicient period to allow the level equalizing action to take place. Thereafter on an increase in load and a corresponding increase in the amount of steam withdrawn, the friction drop between the boiler A and the point of connection of the pipe E is increased with a corresponding decrease in static pressure at that point. The diaphragm E then drops causing the contact E to engage the contact F, energizing the motor F to move the contact bar G downwardly and decrease the resistances in the control circuits of the motors B and C. This downward movement of the lever E causes the container J 6 to be further immersed in the liquid in the container J 4 with a consequent change in the liquid levels in the containers. The increase in value of the control currents and corresponding increase in speed of the motors increases the rate of combustion. The interaction between the floating coil of the Kelvin balance and the stationary coils being proportional to the square of the control current, 'the floating coil is moved upwardly to raise the containers, thus tending to lift, and if the increase in current be sufiiciently great, lifting contact E from the contact However. even if the increase in control current and in rate of combustion is thereupon suflicient to carry the increased load, leakage through orifice J will in time equalize the liquid levels. so that no lifting force will be transferred from container J to container J, which will result in contact E again touching contact F, with a consequent further increase in control current and in rate of combustion. until the container J has again been raised suficient-ly to move the contact E out of contact with the contact F and again interrupt the circuit of the motor F The liquid level equalizing action in the containers continues and the lever is slowly returned into contact with the contact F, unless the steam pressure shall have been sufficiently built up in the boiler by the higher rate of combustion so that the original normal steam pressure is present in pipe E and capable of supporting lever E without aid from the Kelvin balance.

Should the pressure in pipe E rise above normal, as due to a decrease in load, a similar sequence of events takes place in the opposite direction. that is, the contact E first contacts with contact F causing the motor F to raise the bar G. thereby decreasing-the control current and the rate of combustion and permitting coil J and container J to drop and so dragging down lever E and contact E Leakage through orifice J however, shortly removes the efiect of the Kelvin balance, allowing contacts E and F again to engage, unless the steam pressure shall already have dropped suificiently to permit lever E to float in the neutral position without aid or opposition by the coils.

The diaphragm E and Kelvin balance may beproportioned so that the effect of the floating coil is equal to the increase or decrease in friction drop in the steam main A when the control current and the rate of combustion depending thereon have been increased or decreased approximately enough to carry the changed steam flow, inasmuch as the lift of the Kelvin. balance is proportional to the square of the control current and the varying force acting on the diaphragm is proportional to the square of the steam velocity. The tension of the ring J 5 and the spacing of the coils of the l elvin balance are also relatively proportioned so that the floating coil J in its cyclic movements does not contact with either of the stationary coils J. It is apparent that with the compensating means constructed and operating as described, the action of the controller E can be made sensitive and rapid without an undesirable tendency to overshooting and hunting of the controller.

hen the plant shown in the drawing comprises a plurality of boiler furnaces each having its own motors B and C, each of the motors B may have one terminal connected to the supply conductor 1 and may have its second terminal connected to the supply conductor 2 through a resistance R similar to the resistance R and each of the motors C may havev one terminal directly connected to the supply conductor 1 and have its second ter minal connected to the supply conductor 2 through a resistance R similar to the resistance R Thus connected. all of the motors B and C of the battery will be controlled by the same pressure responsive device E and compensating means J, while each of the motors may be independently regulated by its corresponding resistances R and R The damper C is shown as rotatable back and forth between the positions in which it exercises its maximum and minimum flow restricting effects by means of a reversible electric motor L connected to the shaft of the damper C by speed reducing gearing L. The apparatus shown for normally operating the motor L first in one direction and then in the other, and for interrupting its operation arm 0 which is moved to the right on increases, and to the left on decreases, in the temperature to which the thermocouple or o her pyrometer D is subjected. As shown the thermocouple D extends into the furnace chamber at the rear of the bridge wall A of the boiler furnace which is illustrated, by way of example, as of the return tubular type. The instrument 0 is preferably of the well known type employed in recording pyrometers, in which the arm 0 is moved in response to changes in the voltage of the thermocouple D, by a suitable relay mechanism energized from the supply conductors 1 and 2 through a circuit including conductors 12 and 13, whereby the necessary power for giving the arm 0 its proper movement is provided. The arm 0 is frictionally connccted to a switch actuating rod P, as by passing the arm P through an opening in the arm 0 and providing the arm 0' with a spring 0 bearing against movement relative to the arm 0. The rod P is connected to a switch Q having a slight movement between a closed position in which it engages switch contacts Q, and an open position in which it engages a stop Q With the switch Q, in its closed position, a

the right, consequent upon an increase of the temperature to which the thermocouple D is exposed, will move the switch into its open position, but if the movement of the arm 0 to the right thereafter continues. the frictional connection between the arm 0' and rod P yields and permits the rod P to remain stationary without checking the movement of the arm 0. With the switch Q in its open position, a slight movement of the arm 0 to the left consequent upon a decrease in the temperature to which the thermocouple D is subjected, moves the switch Q into its closed position regardless of what the previous actual position of the arm 0 might have been. If the temperature to which the thermocouple D is subjected continues to fall after the switch 0 is closed, the connection between the arm 0: and the rod P yields to permit the continued movements of the left of the arm 0. while the rod P remains stationary in the switch closed position. The switch Q thus opens on any increases in furnace temperature and remains open until the furnace temperature begins to decrease, and on any decrease in furnace temperature the switch closes and remains closed until the temperature of the furnace begins to increase.

The closure of the switch Q connects the terminals of a motor N to the supply conductors 1 and 2 through a circuit including conductors 16, 14, 17 and 15. The motor N is connected by speed reducing gearings N to the shaft of a reversing device or commutator M controlling the direction of rotation of the damper actuating motor L. As diagram matically illustrated, the reversing commutator M comprises a pair of conducting segments M separated from one another by nonconducting segments M.- Bearing on the periphery of the commutator M are a pair of diametrically opposed brushes S and S and an intermediate brush S. The brush S is connected to the conductor 17 and thereby to the supply conductor 2. The brush S is normally connected to one terminal of the winding of the motor L by a conductor 18. The brush S is normally connected to one terminal of a second winding of the motor L by a conductor 19. A common terminal of the two windings of the motor L is normally connected by a conductor 20 to the conductor 16 and thereby to the supply conductor 1. With the commutator in the position shown, the motor L is energized from the supply conductors 1 and 2 to turn in one direction through a circuit including eonductor 17.

brush S, conducting segment Mibrush S,

conductor 20, and conductor 16. In this condition of the apparatus the brush S and conductor 19 are dead. Then the commutator is rotated by the motor N into a position in which either of the conducting segments M are engaged by both of the brushes S and S, the motor L is reversed. lhe energizing circuit for operating the motor L in the reverse direction comprises conductor 1?, brush S,

5 brush S conductor 19, conductor 20, and conductor 16. When this circuit is established, the brush S and conductor 18 are dead.

When the motor L is started into operation in either direction it may be allowed to continue in operation in the same direction regardless of whether the motor N is continuously in operation or not, until the motor N does operate to reverse the direction of rotation of the motor L. Advantageously, however, I provide limit switches T and T to arrest the movement of the motor L whenever required to prevent the damper C from being moved in the closing direction beyond the position in which it exerts its maximum restrictive efi'ect of the flow through the conduit C and to prevent the clockwise movement of the damper G beyond its position in which it exerts its minimum efi'ect on its flow through the conduit 0 As shown the switches T and T are normally closed switches in the motor energizing conductors 18 and 19, respectively, which are engaged and opened when the damper driving gear L moves into corresponding positions, by means of a stud L carried by the gear L As shown, the switch T is normally held in its closed position by a spring T while the switch T tends to close by gravity. Advantageously also, though not necessarily, a switch ll is provided in the common energizing conductor 20 for the motor ,L. This switch is normally held in its closed position by a spring U, but is opened by the indicator arm 0 whenever the latter is moved to the rightinto aposition corresponding to a certain temperature to whichthe thermocouple D is subjected which isconsidered high enough to indicate maximum eificiency of combustion. In the intended operation of the apparatus shown, the speeds of the motor B and G are varied as required to make the general rate of combustion vary in inverse proportion with the pressure of the steam in the main A, in a manner which has been previously explained. Regardless of the general rate of combustion, the damper C is normally in motion tending to increase or decrease the supply of air for combustion to the furnace through the conduit C. When the furnace 0 tion it was being moved when the furnace temperature began to rise, unless and until the damper reaches the corresponding extreme position, whereupon the consequent opening of the corresponding limit switch T .35 or T stops the motor L, and leaves the chamber temperature is rising or is station damper C in its extreme position. On any decrease in furnace temperature, the switch Q is closed as previously explained, and the motor N is then started into operation and continues operation until the furnace temperature again rises. While the motor N is in operation, the consequent rotation of the reversing commutator M reverses the direction of rotation to the motor L at regular intervals.

The motors L and N should have such normal speeds or should be so geared to the damper C and reversing commutator M, respectively, that the time required for moving the damper C continuously in one direction from one extreme position to the other, will be considerably greater than the time required for the motor N, when in operation, to give the commutator M the movement necessary to reverse the motor L. The actual duration of each of those time periods may obviously be varied in accordance with the conditions of operation or the desires of the operator through quite wide limits, but by way of illustration and example, rather than by way of limitation, I may say that I contemplate under some conditions an arrangement in which something like fifteen minutes will be required for the motor L, operating continuously in one direction, to move the damper C from one extreme position to the other, while the motor N, when in continuous operation, will reverse the direction of rotation of the motor L every two or three-minutes.

In the use of my invention as above described, it will be observed that whenever the furnace temperature is falling, the appa ratus operates 'first either to increase or decrease the supplyof air, and then if the temperature continues to fall or remains stationary, it decreases or increases the supply of air, and continues to thus vary the supply of air alternately in opposite directions until finally a condition is reached in which the temperature begins to rise. So long thereafter as the temperature continues to rise or remains stationary, the apparatus operates to vary the rate of air supply in the same direction as brought about the increase in temperature, until the damper C is moved into the corresponding extreme position, unless in the course of such variation the assumed temperature of maximum furnace eficiency is reached, whereupon the switch U is opened.

Whenever a fall in temperature occurs, the apparatus again begins to hunt for the position in which the temperature of the furnace will again increase.

While the hunting which is characterized of the operation of the damper C is generally regarded as undesirable in automatic control apparatus, in the use of my invention this hunting action is desirable because of the manner in'which combustion efliciency depends upon uncontrolled and unrecognizable variations in fuel bed resistance to gas flow therethrough. 1

Certain features of my invention are generically and/or specifically disclosed in my prior application, Serial No. 665,777, filed October 1, 1923, of which the present application is in part a continuation.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the 'art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. The method of operating a furnace which consists in normally exerting a draft changing effect, regularly alternately in direction on any decrease in furnace temperature, until the furnace temperature begins to increase, and thereafter continuously in the same direction.

2. In furnace control systems, the method of maintaining a high furnace efiiciency which comprises normally exerting a draft changing effect varying in one direction, periodically changing the direction of said effect on a decrease in furnace efficiency, and subsequently continuously varying said effect in one direction on an increase in furnace efficiency during said periodic movements.

3. In a furnace control system, the me'thod of maintaining a high furnace efiiciency which comprises normally varying a draft changing efiect in one direction, periodically reversing the direction in which said effect is varied on and during a period of decrease in furnace efiiciency, and subsequently varying said effect in one direction on and during an increase in furnace efliciency.

4. In a steam generator control system, the method of maintaining a high furnace efliciency which comprises varying the rate of combustion in response to changes in steam pressure, continuously varying a draft changing effect in one direction during a period in which the furnace efliciency is at or approaching the desired value. and periodically reversing the direction of variation of said draft changing effect during a period of decreasing furnace efliciency.

5. The combination with a furnace, of a draft regulating device, a reversible motor normally in operation and tending to adjust said device continuously in one direction or the other between extreme positions and means responsive to a condition of furnace efliciency for reversing said motor on a change in said condition indicating a decrease in furnace efficiency.

6. The'combination with a furnace, of a draft regulating device, a reversible motor normally in operation and tending to adjust Said device continuously in onev-direction or the other between extreme positions, and means responsive to the furnace temperature for reversing said last mentioned motor on any decrease in furnace temperature.

7. The combination with a furnace, of a draft regulating device, a reversible motor normally in operation and tending to adjust said device continuously in one direction or the other between extreme positions, means responsive to a condition of furnace efiiciency for rei'ersing said motor on a change in said condition indicating a decrease in furnace efficiency, and for stopping said motor when said conditions indicate a predetermined relatively high efliciency.

8. The combination with a furnace of a draft regulating device, a reversible motor normally in operation and tending to adjust said device continuously in one direction or the other between extreme positions, a reversing mechanism for said motor including a second motor, and controlling means for said second motor responsive to a condition of furnace eificiency for starting and stopping said last mentioned motor on changes in said condition indicating a decrease or an increase, respectively, in the furnace efficiency.

9. In a furnace regulating system, the combination with an electrical thermometric device responsive to the furnace temperature, an'electrical instrument connected to said de vice and comprising a part moving to and fro accordingly as the furnace temperature increases and diminishes, and a combustion regulating means including an actuator, means limiting the movements of said actuator, and a yielding connection between said part and actuataor whereby the movement of said part is not limited by the limitation of the actuator movements, but an initial movement of said part in either direction produces a corresponding movement of said actuator.

10. The combination with steam generating apparatus and a main receiving steam generated thereby, of a combustion control system including a movable member, means connected to said member and to said main at a point at which the steam pressure varies in response to changes in load, means for varying an electrical control current in accordance with the movements of said member, and means actuated by said control current and temporarily applying a force on said member tending to return the latter to an original normal position.

11. The combination with steam generating apparatus and a main receiving steam generated thereby, of a combustion control system including a member moving in response to changes in steam pressure at a point in said main at which the steam pressure varies in response to changes in load, means responsive to the movements of said member for adjusting an electrical control current, and means actuated by said control current anplving a force tending to restore said member to an original normal posit-ion including a yieldable transient connection between said last mentioned means and said member.

12. The combination with steam generating apparatus and a main receiving steam generated thereby, of a combustion control system including a member moving in response to changes in steam pressure at a point in said main at which the steam pressure "aries in response to changes in load, means responsive to the movements of said member for adj usting an electrical control current, and means actuated by said control current applying a force tending to restore said member to an original normal position including a progressively yielding connection between said last mentioned means and said member.

13. The combination with steam, generating apparatus and a main receiving steam generated thereby, of a combustion control system including a member deflecting in response to changes in steam pressure at a point in said piping at which the steam pressure varies in response to steam load, means for progressivley changing an electrical control current in accordance with the movement of said member on a change in steam load, and means responsive to the control current and acting temporarily to apply to the deflecting member a restoring force which is initially proportional to the change in the control current.

14; The combination with steam generating means and a main receiving the steam generated, of a combustion control system there for comprising means for maintaining a regulable electrical control force, the latter means including a balanced element moving in response to steam pressure in said piping at a point at which the steam pressure changes in response to changes in the rate of steam delivery and to changes in the pressure at which the steam is generated, an electrical regulator operative on a predetermined movement of the balanced element from a normal position to vary the electrical control force in accordance with changes in steam pressure, a restoring means through which the control force acts upon the balanced element, and means gradually eliminating the action of said restoring means after a change in control force.

15. In a boiler combustion control system, means for creating an electrical control current comprising a balance, means for subjecting said balance to a pressure which is less than the boiler steam pressure by an amount which is a function of the steam outflow from the boiler, means for subjecting said balance to a constant opposing force sutficient to neutralize the action on the balance of the first mentioned force when the latter is equal to the normal boiler steam pressure, means for subjecting said balance to an electro-magnetic force created by said control current and acting on said balance in the same direction as the first mentioned force, a current regulator actuated by said balance to increase and decrease said control current accordingly as said constant force overbalances or underbalances the joint action on the balance of the other two forces, and means whereby theaction of said electro-magnetic force is gradually eliminated subsequent to a change in the control current. v

16. In a boiler furnace combustion control system, the combination with draft and fuel feed regulating mechanisms, ofmeansresponsive to a condition of boilerload for effecting adjustments of said mechanisms tending to maintain fuel and draft feedsproportioned to one another and to the boiler load, means normally eifecting adjustments of the draft feed regulating mechanism tending to continuously vary the volume of draft, first in one direction and then in the opposite direction, and means responsive to a condition of boiler efficiency for reversing the direction of draft change produced by the second mentioned means on a predetermined change in said boiler eificiency.

17. In a boiler furnace combustion control system, the combination with draft and fuel feed regulating mechanisms, of means responsive to a condition of boiler load for efiecting adjustments of said mechanisms tending to maintain fuel and draft feeds proportional to one another and to the boiler load, means normally effecting adjustments of the draft feed regulating mechanism tending to alternately and progressively increase and decrease the volume of draft, and means responsive to the boiler furnace temperature for re versing the direction of draft change produced by the second mentioned means on a decrease in said temperature. 7

18. In a boiler furnace combustion control system, the combination with draft and fuel feed regulating mechanisms, of means responsive to a condition of boiler load for adjusting said mechanisms to increase and decrease the fuel and draft feeds on increases and decreases respectively in the boiler load, means normally adjusting the draft regulating mechanism to continuously vary the volume of draft first in one'direction and then change produced by the second mentioned means.

19. In a boiler furnace combustion control system, the combination with draft and fuel feed regulating mechanisms, of means responsive to a condition of boiler load for adjusting said mechanisms to increase and decrease the fuel and draft feeds on increases and decreases respectively in the boiler load, means normally adjusting the draft regulating mechanism to continuously vary the volume of draft first in one direction and then in the opposite direction, and means automatically responsive to a condition of boiler eiiiciency for reversing the direction of draft change produced by the second mentioned means one or more times during each period in which the boiler efficiency is diminishing, and means thereby operating during any period in which the boiler efliciency is diminished for periodically reversing the direction of draft change produced by the second mentioned means.

20. The combination with a furnace of a furnace draft regulating device, a reversible motor normally in operation and tending to continuously adjust said device and thereby alternately increase and decrease the furnace draft, and means responsive to the variations in the furnace temperature for reversing said motor on a reduction in said temperature.

21. In a boiler furnace regulating system, the combination with a combustion regulating device, of means comprising a movable member subjected to a force proportional to the boiler header steam pressure, means subjecting said member to a constant loading force opposing said thrust and normally holding said member in a neutral position, means actuated by a movement of said member to maintain a force which controls said device and which is increased or decreased by a movement of said member away from its normal position accordingly as said movement is due to a decrease or an increase in said pressure and correspondingly actuates said devices, a member moved on variations in said control force into different positions corresponding to different values of said force, and a dash pot connection between said members.

22. In a boiler furance regulating system, the combination with a combustion regulating device, of means comprising a movable member subjected to a force proportional to the boiler header steam pressure, means sub jecting said member to a constant loading force opposing said thrust and normally holding said member in a neutral position, means actuated by movement of said member to maintain a force which controls said device and which is increased or decreased by a movement of said member away from its normal position accordingly as said movement is due to a decrease or an increase in 

